To date, efforts to develop clinically viable in vivo chemical sensors for real-time monitoring of blood gases, electrolytes, glucose, lactate, etc. in critically ill hospital patients have been stymied by the inaccurate analytical results obtained owing to sensor biocompatibility problems (cell adhesion, thrombus formation, inflammatory response, etc.). The goal of this research program is to explore and optimize the chemistries required to fabricate in vivo chemical sensors with outer polymeric coatings that slowly release or generate low levels of nitric oxide (NO). The local release/generation of NO mimics the chemistry that occurs at the inner walls of all healthy blood vessels (NO production by endothelium) and is expected to greatly enhance the biocompatibility and concomitant analytical performance of the implanted sensors. Indeed, results during the first 3 phases of NIH support have clearly demonstrated that in situ release and/or generation of NO significantly reduces surface thrombus formation and improves in the in vivo analytical accuracy of intravascular oxygen sensors, and also reduces inflammatory response for glucose sensors implanted subcutaneously. Newly developed NO generating polymers, based on spontaneous catalytic decomposition of endogenous S-nitrosothiols (RSNOs) at immobilized Cu(II) or organoselenium (RSe) sites, are potentially the most attractive coatings for preparation implanted sensors. However, any significant variability in endogenous levels of RSNOs in blood may ultimately dictate whether these NO generation type polymers can provide results equivalent to NO release coatings (with NO donors doped or covalently linked to polymers). Therefore, in the final phase of studies, the most promising NO release and NO generation coatings will be evaluated side-by-side via in vivo studies with coated sensors implanted intravascularly (arteries and veins) within pigs and rabbits. Beyond oxygen sensors, greater emphasis will be placed on also demonstrating improved biocompatibility/performance for intravenous glucose and lactate electrochemical sensors prepared with these coatings. Such sensors are sorely needed in the ICU and other critical care hospital units where tight glycemic control of patients significantly improves outcomes, and where trends in blood lactate levels are viewed as an important prognosticator of patient recovery. Measurements of RSNO species in the test animals with improved electrochemical RSNO sensors will also be carried out to assess whether there is a clear correlation in analytical performance/thrombus formation for sensors prepared with the NO generating coatings vs. measured RSNO blood levels. The ability to reliably measure critical care analytes (blood gases, electrolytes, metabolites) in blood continuously at a patient's bedside is the holy grail for biomedical sensor technology, and this goal can only be achieved when sensor performance is not compromised by biocompatibility issues. Hence, the success of this research will have significant impact in the ability improve the quality of health care for critically ill patients.